The way in which fuel is injected into the cylinders determines the torque, fuel consumption, emissions and noise of diesels. Two factors are important: the fuel pressure as it enters the cylinder, and the shape and number of the injections.

A common-rail injection system separates the two functions - generating pressure and injecting - by first storing the fuel under high pressure in a central accumulator rail, then delivering it to the individual electronically-controlled injection valves (injectors) on demand. This ensures that incredibly high injection pressures (over 25,000 pounds per square inch in some systems) are available at all times, even at low engine speeds.

Sample Common Rail System

All internal combustion engines need two key ingredients to operate: air and fuel. The precise delivery of these ingredients is what makes clean and powerful combustion possible. Just as turbochargers help deliver copious amounts of air to help diesels operate cleanly, efficiently and powerfully, the parallel revolution in fuel delivery has ushered in the renaissance of diesels in Europe.

High fuel pressure produces a fine mist of fuel that burns better and cleaner in the combustion chamber. Not only that, but for each combustion cycle, the common rail allows up to five injections per cycle. The driver benefits as lower fuel consumption (improved mpg), better engine performance and less noise than with older diesels.